Male lemurs are able to signal their genetic quality through an olfactory cue. The perfume attracts females and provides the basis for their choice of reproductive partner.

Olfaction, little studied in primates until now (1), is a significant means of communication in certain monkeys, and especially in lemurs. These mammals, which live almost exclusively in Madagascar, include more than thirty species. One of the best known is the ring-tailed lemur, Lemur catta, a highly social species that lives in small, female-dominated groups. In this species, olfactory communication plays an essential role in social relations.

The Lemur catta male possesses three sets of glands that produce scent molecules, including scrotal glands on the testicles. Marie Charpentier, researcher at the Centre d'écologie fonctionnelle et évolutive (2), and her colleagues at Duke University (3) were interested in olfactory communication in these primates. They studied the scents released from the glands of 19 adult males living in a semi-free colony at the Duke Lemur Center. They discovered that the chemical diversity of secreted odors was correlated with the genetic diversity of the individual. The greater a male's genetic diversity (the more heterozygous (4) he is), the more complex his olfactory message (the scent molecules are released more frequently and abundantly).

Surprisingly, this phenomenon is only observed during the breeding season, a relatively stressful time for males who are in competition for females. The females, for their part, have to make a good reproductive choice, and to this end, they pick out the males that are the most heterozygous -- a sign of health -- by their ability to diffuse a complex bouquet of scents. This signal enables females to evaluate the genetic worth of males and to choose the one with the best qualities to pass on to offspring.

Another important result: the less related two males are in terms of their scent, the less they are related genetically as well. The olfactory signal therefore carries a second message of how closely two individuals are related. Again, this correlation is only detectable during the breeding season, precisely when individuals are in competition.

Christine Drea received funding for this work from the National Science Foundation.